Idiopathic pulmonary fibrosis (IPF) is an ultimately fatal disease, characterized by progressive scar tissue formation leading to respiratory failure. There is a strong association between aging and IPF, however few studies have investigated the effects of aging on susceptibility to persistent lung fibrosis. Our preliminary studies indicate that aged mice exhibit persistent fibrosis in response to lung injury. We previously reported a critical role for NOX4/H2O2 in mediating myofibroblast functions and lung fibrosis. However, age-associated alterations in NOX4 expression as well as the role of NOX4/H2O2 in mediating pro-fibrotic lung myofibroblast phenotypes (senescence, apoptosis-resistance) have not previously been reported. The proposed studies, we will explore the hypothesis that, in the context of aging, NOX4 contributes to persistent fibrosis by the accumulation of senescent myofibroblasts, which may then induce apoptosis of epithelial cells. We propose to develop a novel animal model of persistent fibrosis in aged mice, which more accurately mimics the persistent/progressive fibrosis seen in IPF patients. These studies will provide: (1) more relevant ex vivo and in vivo experimental models for investigation of IPF and pre-clinical evaluation; (2) novel insights into the role of aging andin the pathogenesis of IPF; and, (3) expanded roles of NOX4/H2O2 in aging and further proof-of-concept for therapeutic targeting NOX4 in fibrotic diseases.